The 0.223 caliber cartridge is the accepted standard for use in military weapons in nearly, if not all, the major countries of the world. While the weapons themselves may differ from one country to another, the cartridges do not. On the other hand, all of the North Atlantic Treaty Organization (NATO) countries use even the same weapon.
The cartridge case carrying the 0.223 caliber bullet is much larger and it also tapers from a diameter of approximately 0.375 inch at its rear end where the extractor groove and rim is located on down to about 0.350 inch at the point where it is "necked down" to the size of the bullet thus leaving an annular shoulder. The taper of the shell casings is such that they will not stack vertically as some cartridges will that have more or less cylindrical casings with no rim on the rear end of larger diameter. Accordingly, in order for these tapered shell casings to stack atop one another, the magazine holding them must either be curved or have an angled bend adjoining a pair of straight sections positioned both above and below the latter. It makes little difference whether the stack is a single shell wide, is staggered or perhaps even made up of two rows side-by-side, the magazine must be either curved or bent at a point intermediate its ends to accommodate the tapered shell casings.
Of course, the standard version of the magazine used by the U.S. military in its M16A2 automatic rifle is configured to accommodate the aforementioned tapered shell casings and, presumably, any magazine developed for use in this or any other similar weapon will have to be similarly shaped along with being designed to fit into the firing chamber. Unfortunately, the ones in current use have a rectangularly-coiled helical spring in the bottom to lift the follower which limits the capacity of the unit and, most significant of all, makes them prone to jam. The jamming problem is so acute that the instructors teaching the use of the weapon oftentimes advise the soldiers to load no more than eighteen shells in a twenty shell clip or twenty-five shells in a thirty shell one. Of course, the more shells a clip will hold and feed effectively, the greater the fire-power and effectiveness of the weapon.
The problem with the present clips no doubt stems, in part at least, from the use of the helical spring to lift the follower and shell stack since as it expands it loses much of its biasing force even though the load of the shells in the stack thereabove becomes successively lighter. Also, springs of this type when tightly compressed oftentimes exceed their load limit and thus lose their ability to lift the shell stack and push the shells into the chamber. Whatever the reason, the clips presently in use are unsatisfactory.